Light extraction efficiency of light-emitting diodes (LEDs) has become an important topic in improving brightness. A variety of conventional skills has been focused on the research of the surface roughening of LED chips for increasing the light extraction efficiency of LED chips. For example, texturing the top or bottom surface of the substrate by wet etching or dry etching for improving the scattering effect of the substrate, or roughening the top surface of the epitaxial structure by etching or growth method such that more light can be extracted from the top side of the LED chip have been tried to improve the light extraction efficiency of LED chips themselves. In addition, an adapted package form also plays a role in helping LED chips to achieve excellent light extraction efficiency.
FIG. 1 shows an conventional SMD (Surface Mount Device) type LED apparatus 10 comprising a submount 11 having a first conductive line 111 and a second conductive line 112, an LED chip 13 formed on the central portion of the submount 11, a reflecting cup 12 formed on the submount 11 and enclosing the LED chip 13, and a transparent encapsulating material 14 filled in the cavity formed by the reflecting cup 12 for encapsulating the LED chip 13. The light-emitting chip 13 comprises a first electrode (not shown) and a second electrode (not shown) electrically connected to the first conductive line 111 and the second conductive line 112 correspondingly by separate wires 19. The first conductive line 111 and the second conductive line 112 are extended from the top surface to the bottom surface of the submount 11 for mounting on a printed circuit board (PCB). The reflecting cup 12 redirects the light emitted from the LED chip 13 upwardly to form a directional light beam. Having the whole cavity filled with the transparent encapsulating material 14, part of the light is not able to transmit through the transparent encapsulating material 14 due to the total reflection at the interface between the transparent encapsulating material 14 and the ambient surroundings. Besides, it is difficult to dissipate the heat generated from the LED chip 13 through the reflecting cup 12.
U.S. Patent Publication No. US2005/0067628 proposes a way to overcome the abovementioned problems. As shown in FIG. 2, a transparent encapsulating material 24 encapsulates only an LED chip 23 such that the majority of light is able to pass through the transparent encapsulating material 24, and the probability of total reflection is significantly lowered. However, part of light is still confined within the reflecting cup. Moreover, spaces are formed between the reflecting cup 22 and a cup supporter 221 for disposing some peripheral electronic elements and it is difficult to dissipate the heat generated from the LED chip 23 through the reflecting cup 22.
In view of the above, the invention proposes a light-emitting apparatus for improving the light extraction efficiency and the heat dissipation.